Process for producing zirconium chloride



7 June 15, 1948. w. J. KROLL EI'AL PROCESS FOR PRODUCING ZIRCONIUMCHLORIDE Filed April 12, 1944 INVENTORS WILLIAM J. KROLL FREDERIC E.BACON ATTORNEY Patented June 15, 1948 UNITED STATE$ ATENT FFlCE PROCESSFOR PRODUCING ZIBCONIUM CHLORIDE Application April 12, 1944, Serial No.530,752

3 Claims.

This invention relates to the preparation of zirconium, and morespecifiically refers to a novel process for preparing fromzirconium-silicon al loys. zirconium chloride and, therefrom, zirconiumof commercial quality. This application is in part a continuation of ourapplication Ser. No. 502,041, filed September 11, 1943, now abandoned.

The principal use for zirconium in the metallic state is in themanufacture of steel. For that use ferrozirconium, which ordinarilycontains silicon, and the zirconlum-silicon-iron alloy usually termedsilicon-zirconium, are quite satisfactory and are widely available inseveral commercial grades.

A purer form of metallic zirconium is demanded for some other uses, forinstance in the manufacture of nonferrous alloys. The demand hasenerally been met commercially by reducing zirconium compounds withcalcium or sodium or by a vapor phase decomposition of zirconiumhalides. Although these methods yield zirconium of good quality, theyrequire relatively expensive iron-free zirconium salt as the rawmaterial.

An object of this invention is to produce zirconium of high quality byan economical process which may use relatively inexpensive and readilyavailable raw materials. A further object is a novel method forproducing substantially ironfree zirconium chloride suitable for use toproduce a good grade of zirconium. Another object is to provide a novelprocess for producing zirconium of high quality fromzirconium-siliconiron alloys of ordinary commercial purity, such assilicon-zirconium and ferrozirconium.

In its most general aspect the method of the invention comprisescontacting a zirconium-silicon alloy with an anhydrous metal halidewhich has a materially smaller heat of formation than the correspondingzirconium halide, preferably with iron chloride, at an elevatedtemperature below the melting point of the alloy, to form zirconiumhalide.

The alloy should be in a finely-divided state, preferably fine enough topass a 100 mesh screen. The zirconium content of the alloy is notcritical, and may be as low as and up to 50% or more.

One manner of practicing the method of this invention comprisesintimately mixing, in the solid state, zirconium-silicon-iron alloy andferrous chloride; heating the mixture to a reaction temperature aboveabout 220 C. and below the melting point of the ferrous chloride,thereby gen rating vapors of zirconium chloride and silicon chloride;and separating and recovering the zirconium chloride which may then bereduced to zirconium. Preferably, the separation and recovery isefiectecl by passing the chloride vapors through a mass of salt whichselectively removes the zirconium chloride; but as an alternative thezirconium chloride may be condensed at a temperature at which siliconchloride is still in the vapor phase.

To obtain an intimate mixture, the zirconium silicon-iron alloy andferrous chloride should be oomminuted and intermingled, and arepreferably briquetted. Preferably, no binder is used in forming thebriquettes. The briquettes may be small, for instance about the size oflarge lima beans, or large, for instance two inches in diameter b twoinches high.

The invention will be described more specifically herein with referenceto the accompanying drawing which illustrates, by way of example only, asuitable apparatus for carrying out the method of the invention.

The briquettes, or alternatively a loose mixture of the powderedingredients, are charged into an upper compartment III of the apparatusillustrated. In a lower compartment II, which is in communication withthe upper compartment I 0, there is placed a quantity of molten salt I5comprising one or more alkali metal halides, preferabl a mixture ofsodium and potassium chlorides in the weight ratio of about 2 partssodium chloride to 3 parts potassium chloride, melting below 650 C. Anatmosphere of hydrogen or other gas inert under the conditions of theprocess is maintained within the apparatus by introducing a stream ofsuch gas through an inlet I 2 to the upper compartment and withdrawingit through an outlet I3 at the top of the lower compartment. A tube I4leads effluent gases and vapors from the upper compartment it into thebody of salts I5 in the lower compartment II. To avoid contamination ofthe salts I5, it is preferred to construct the tube I4 of graphite, andalso to contain the salts I5 in a graphite pot I6.

The entire apparatus just described is heated, for example in a furnaceIT, to a temperature sufficiently high to initiate a reaction betweenthe ferrous chloride and silicon-zirconium-iron alloy and to maintainthe salt I5 molten. The reaction will be initiated at a temperaturesomewhat above 200 C., usuall between 220 and 250 C. The reaction isstrongly exothermic and the temperature will rise rather rapidly,reaching a maximum in the neighborhood of 1l00 or 1200 C. in an hour ortwo.

The reaction forms zirconium chloride and and the zirconium chlorideremains in the salts 55. If the briquetted material contains asimpurities aluminum or titanium, any chlorides of aluminum as well asany iron chlorides which. may be evolved in the upper compartment andpassed into the lower compartmentare dissolved in the salts in the lowercompartment; 'but'titanium chlorides are not dissolved.

a handicap to theiruse. Instead of using a salt 1 or salts to absorb thezirconium chloride, an ordinary condenser may be used. If the condenseris maintained at a suitable temperature between 57 C. and 331 C., onlythe zirconium-chloride will be condensed.

In a typical example of'the 'method hereinbefore described, 455 poundsof 'a briquetted mixture containing 18.25 pounds ofzirconiumsilicon-iron alloy and 27.25 pounds of ferrous chloride wereplaced in the upper compartment l0, and 26.4 pounds of a mixture ofpotassium chloride and sodium chloride in a weight ratio of 3 to 2 wasmelted in a graphite :pot and placed in the lower compartment H. Thezirconiumsilicon-iron alloy contained 36.8% zirconium, 47.5% silicon,remainder iron. The apparatus was heated, gas evolution started at 220C. (measured by a thermocouple in the centerof the upper compartment andin 1.5 hours it reached a, maximum of 1:160 :C. After a total of twohours, the salts were-removed and' were found to contain 3.61 pounds-ofzirconium as zirconium chloride, representing an efficiency of 53.6%.The residue in the upper compartment [0 contained 2.77 pounds ofzirconium, losses and unaccounted for being only 0.36 pound or 5.4%.

According to an alternative procedure, which may be carried out insimpler apparatus, zirconium-silicon-iron alloy and 'iron chloride areadded to a molten bath comprising one or more chlorides of metals havinga high affinity for chlorine, for instance sodium, potassium, lithium,calcium, barium, or magnesium. Such dilution ;decreases fuming and tendsto modify the violence of the reaction. A particularly useful diluent isa mixture of potassium chloride and sodium chloride in a weight ratioapproximating 3.to 2. These salts do not take part'in the reaction'andact as solvents only; they "retain the zirconium chloride but not thesilicon chloride.

The molten salt bath mixture may appropriately be held between 650 and105'0 C. in a covered crucible. Within'this range of temperatures thereaction is satisfactorily rapid.

Ferric chloride reacts rather violently :with

high-zirconium zirconium-silicon alloys. Therefore, if the latter alloysare used, ferrous chloride is the preferred reactant, although theferric salt may be used to react with low-zirconium alloys, withprecautions against explosively violent reaction.

In a=specific instance of the'pra'ctice of this alternative modificationof the invention, 300 parts by weight of zirconium-silicon containing37% zirconium and about 45% silicon, remainder iron, powdered to pass amesh screen, was heated .for one-half hour at 700 C. in a bath composedof "1200 parts by weight of potassium chloride and 285"parts of ferricchloride. The result was an iron-silicon sludge and a salt mixturecontaining as zirconium chloride 68% of the zirconium originally in thezirconium alloy. The iron con tent of the salt mixture was only 0.1%.Some silicon chloride was formed as a by-product and volatilized.

Most of the salt is easily separatedfrom the iron-silicon sludge residueby decantation. The rest may be removed by vacuum distillation.

If pure zirconium chloride is desired as an intermediate or end product,it is distilled from the salt bath. Usually, zirconium metal will bedesired, and this requires a further step of the process.

In the further step of the process 'of this invention, the molten saltmixture containing zirconium chloride resulting from the first step, aspracticed by either of the alternatives described. is contacted withmetal of thegroup consisting of the alkali metals, the alkaline earthmetals, and magnesium, a preferred reagent for this step beingmagnesium. These metals, having a far greater aifinity than zirconiumfor chlorine, replace the zirconium in the chloride and precipitatezirconium in powdered form. After the reaction, most of the salt isdecanted'for reuse, the resulting mixture of zirconium and salt iscooled and broken up, and the salt is removed by vacuum distillation orby washing with water. The reaction will readily go practically tocompletion, leaving only a very low concentration of zirconiumchloridewhich may be recycled.

We claim:

1. Process for producing zirconium chloride which comprises reactingsolid ferrous chloride and solid zirconium-silicon alloy, in the absenceof other chlorinating agents, at a temperature above the volatilizationtemperature of the chlorides of silicon and zirconium and in the range220 C. to 1200 C., but for a substantial period of time not rising abovethe volatilization temperature of ferrous chloride, so as to produce amixture of the vapors of zirconium chloride and silicon chloride andthen passing the mixture into molten alkali metal chloride whichdissolves only the zirconium chloride.

Process for producing zirconium chloride which comprises reacting abriquetted mixture of comminuted solid ferrous chloride and comminutedsolid zirconium-'silicon-iron alloy, in the absence of otherchlorinating agents, at a temperature above the volatilizationtemperature of the chlorides of silicon and zirconium and in the range220 C. to 1200 C., but for a substantial period of time not'rising abovethe volatilize.- tion temperature of ferrous chloride, so as to producea mixture of the vapors of zirconium chloride and silicon chloride andthen passingthe mixture into molten alkali metal chloride whichdissolves only the zirconium chloride.

3. Process for producing "zirconium chloride which comprises reacting abriquetted mixture of comminuted solid ferrous chloride and comminutedsolid zirconium-silicon-iron alloy, in the absence of other chlorinatingagents, at a temperature above the volatilization temperature of thechlorides of silicon and zirconium and in the range of 220 C. to 1200C., but for a substantial period of time not rising above thevolatilization temperature of ferrous chloride, so as to produce amixture of the vapors of zirconium chloride and silicon chloride andthen passing the mixture into a molten mixture of sodium and potassiumchloride which dissolves only the zirconium chloride.

WILLIAM J. KROLL.

FREDERICK E. BACON.

REFERENCES CITED The following references are of record in the file ofthis patent:

organic and Theoretical Chemistry, vol. 7, pages 101, 107, 108, 143,144. Pub. by Longmans, Green and Co., London (1927).

